The use of radar systems on aircraft for detecting other aircraft arose almost as soon as radar itself was devised, and that use has expanded to detection of ground targets. Range and clutter advantages arise from operating a radar system from a high and open location free from obstacles. The shape and aerodynamic requirements of aircraft make it difficult to attach the necessary antennas to the aircraft. Additionally, the antenna(s) must be suitable for both of the major radar functions which are required, namely volume search to identify targets anywhere in the relevant airspace, and tracking to maintain contact with particularly important targets. The types of antennas for these different functions are different.
Airborne Warning and Control System (AWACS) aircraft typically use either (a) one or more conformal antenna arrays affixed to the exterior of the fuselage or body of the aircraft, (b) one or more linear arrays located in a rotational disk-like structure mounted above the fuselage, where the rotation provides the 360° azimuth coverage required for surveillance applications, or (c) an array located in the nose of the aircraft. The conformal array approach orients the antenna parallel to the longitudinal axis of the aircraft, in which position, generally speaking, the antenna beams point laterally relative to the aircraft. This lateral radar coverage makes forward-looking performance difficult to obtain. The rotating-disk technique suffers from aerodynamic limitations, and an antenna contained in such a disk cannot be as large as might be desired to achieve the desired beamwidth(s). The nose location severely limits the possible aperture of the antenna and therefore limits the beamwidth.
Improved or alternative airborne radar arrangements are desired.